1. Field of the Invention
This invention relates to a plug-in cartridge with active carbon brushes for commutator type motors, particularly such a cartridge which permits easy and safe replacement of worn active carbon brushes. Another object of this invention is to provide such a cartridge which is economical to manufacture.
2. Description of the Prior Art
Non-metallic pistol handle type power tools make easy access to active carbon brushes virtually impossible as it is usually necessary to partially dissemble the tool to gain access to at least one of the brushes. An example is "The Care and Operation" manuals distributed by Milwaukee Electric Tool Corporation, the assignee of this application, identified as 58-12-0840 and 58-12-0675. The first of these manuals states that the second brush "can be exposed by removing the six screws which secures the right side of the pistol grip". It appears to be necessary to "liftout trigger switch assembly and remove lower brush cap". However, the second manual makes it clear that with aluminum handle type drills both brushes may be individually and separately removed without disassembling the body for the motor.
When the brushes are mounted in the housing of power tools with metal pistol handles or in metal bell housings of conventional electric motors, each of the two brush holders and carbon brushes may be separately and individually removed. For examples, see the following U.S. Pat. Nos:
1,443,499: PA1 3,162,782: PA1 3,362,111: PA1 3,369,615: PA1 3,381,104: PA1 3,441,766: PA1 3,489,191: PA1 3,513,343:
2,372,660:
3,450,917:
3,617,786.
The results of a patentability search did not uncover any patent which disclosed a plug-in cartridge which carried both of two actice brushes positioned to engage the motor commutator at diametrically opposite positions. U.S. Pat. No. 1,443,499 appears to disclose a non-plug-in type cartridge carrying two brushes. U.S. Pat. No. 3,496,394 also discloses a non-plug-in type cartridge carrying two brushes. Perhaps the most pertinent disclosure pertaining to a plug-in cartridge is U.S. Pat. No. 3,387,155. However, the brushes carried by such cartridge do not engage the commutator at diametrically opposite positions.
Another prior art recently known to applicant is U.S. Pat. No. 3,813,567. This patent shows and describes a carbon holder 9 seated on the outer end of a casing 8 (see FIG. 2). The holder 9 and two brushes 15 mounted on it can be removed after the removal of a housing cover 12 and its plurality of holding screws 11. The removal of the cover 12 also withdraws the rotor 13. Hence, when the brush holder is removed, the brushes 15 are not removed from the commutator. There is no description of how the brushes 15 are held retracted when the rotor 13 with its commutator is axially removed with the cover 12. Thus, this patent does not disclose a plug-in cartridge.